The overarching purpose ofthis Center Grant, Alternative Formulations of Tenofovir and UC781 is to develop and compare the performance of two contrasting vaginal microbicide formulation approaches, a gel and a film, as carriers for an antiretroviral drug combination, UC781 and tenofovir (TFV). This project, Project 4, quantitatively explores the PK domain in exploratory clinical studies by way of direct and non-invasive sampling of 6 different compartments within the body - fluid and CD4+ cells components both within the cervicovaginal lumen, cervicovaginal tissues, and blood. The spatlotemporal drug concentration data gathered will be evaluated in light of pharmacodynamic (PD) data, both efficacy and toxicity, from this and other Projects within the Center Grant. Armed with this PK-PD data investigators can reach informed decisions about (1) continued development of these two combination products, (2) potential modifications of the eventual product candidates tested, and (3) rational study design as the candidates enter formal clinical testing. To achieve these objective, we have the following 4 specific aims: Aim 1. Develop and validate assays for UC781, improve tenofovir intracellular assay sensitivity in clinical samples, and verify compatibility of radiolabels with film formulations (Supports Aim 3 & 4 clinical studies) Aim 2. Determine the feasibility of using quantitative changes in cervicovaginal permeability to small molecules and HIV-size particles as a measure of candidate microbicide toxicity: an open label, exploratory clinical study comparing nonoxynol-9 gel to universal placebo. (Needed for support of Specific Aim 3). Aim 3. Compare the spatlotemporal distribution (cervicovaginal and systemic) of candidate film and gel formulations of UC781 (Aim 3-1) and TFV (Aim 3-2): an exploratory clinical study. Aim 4. Exploratory Human and Macaque PK-PD relationships. Perform drug assays from pharmacodynamic (efficacy and toxicity) studies in macaques (Project 2) and humans (Project 3) and develop exploratory pharmacokinetic-pharmacodynamic (PK-PD) models to describe the drug exposure-response relationships for each candidate microbicide (UC781 and tenofovir) and formulation.